Resonant Faraday rotation measurements in a potassium vapor cell*

The Faraday effect, a magneto-optic rotation induced by a circularly birefringent medium, manifests itself as a rotation in the plane of polarization as light traverses through it. This investigation centers on applying the resonant Faraday effect, for probing the magnitude of external magnetic fields.

For this study, a tunable diode laser operating at a wavelength near the potassium D2 line (766.7 nm) is employed. A potassium vapor cell is positioned inside a uniform magnetic field (approximately 5-10 G) generated by a pair of Helmholtz coils. Using PEM ellipsometry, a basic polarizer-analyzer optics setup, and modulation techniques, we extract changes in polarization as the laser beam interacts with Zeeman-shifted potassium atoms—typically measured less than 100 millidegrees. A temperature stabilization of the potassium vapor cell within 0.1°C keeps the vapor density stable enough to measure the Faraday rotation angle and therefore the magnitude of the external field with high precision.

The primary objective of this study is to explore the potential application of the resonant Faraday effect in probing the polarization dynamics of helium-3 within hybrid Spin Exchange Optical Pumping (SEOP) cells. Progress on the status of the experiment will be presented.